The power for the primary side control circuits of a switching converter may be conveniently obtained from a tertiary winding of the power transformer. This power is used to energize primary control logic circuits and to provide base drive signals for the power semiconductor switching devices. Should the voltage on the tertiary winding drop, the base drive signals to the power switching devices could drop to a low level so that the switch is operated in its active region. In the case where the low voltage is caused by an output fault, the high currents induced in the power switching device, while it is in the active region, could cause it to fail.